The Internet Group Management Protocol (IGMP) is a communications protocol used to manage the membership of Internet Protocol multicast groups. The IGMP is used by IP hosts and adjacent multicast routers to establish multicast group memberships. As an example, when an IP host intends to join a multicast service that is corresponding to one multicast group, it uses the IGMP to join the multicast group. Furthermore, IP hosts use IGMP to report their multicast group memberships to any immediately-neighboring multicast routers. Multicast Listener Discovery (MLD) is an equivalent protocol for the host-router part in IPv6.
The report message is triggered in two cases. When the host wants to receive a multicast stream, it sends an unsolicited membership report message for joining that group to the local router. Another case is that the host generates a report message of its interested groups in response to a Query message.
The leave report message is specified by IGMPv2, which is sent by a host when it leaves a multicast group. This allows group membership termination to be quickly reported to the router.
Multicast routers use IGMP to learn which groups have members on each of their attached physical networks. The router keeps a list of multicast group membership for each attached network, and maintains the list by periodically sending host membership query messages to the all-hosts group address 224.0.0.1. If no membership report message of a specific multicast group responsive to the sent query message is received within a predetermined time, the router assumes that no host is receiving the multicast service associated with the multicast group. And as a consequence, the record of the multicast group will be deleted and the corresponding multicast packets will not be routed to the sub-network. Herein, the “multicast group membership” means the presence of at least one member of a multicast group. And the router need not keep a list of hosts that are receiving the multicast service.
A wireless communication network, such as IEEE 802.16 (WiMAX, World inter-operability for Microwave Access), can make use of IGMP to manage multicast group. However, due to such factors as time-variant fading and burst error, the air interface between the receiving device such as a Mobile Station (MS) and the access device such as a Base Station (BS) is usually unreliable. As a consequence, the IGMP related messages are lost or not correctly received, which may result in service interruption.